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      12-31-2020, 04:20 PM   #1
socalengineer
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Lowered suspension as close to OEM ride as possible

Hi All,

Which suspension would you recommend if you wanted the car to be lower but to have as good ride comfort as the OEM suspension?

I was thinking Billstein B12 Pro-Kit, or Ksport suspension. Because both of those use monotube shocks with progressive springs, which is the same design as OEM shocks/springs.

Thoughts?
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      01-03-2021, 05:13 PM   #2
doggboy
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Just get some Eibach springs. They are just as comfortable as stock, in fact I would have preferred them to be a bit more stiff.
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      01-04-2021, 04:26 AM   #3
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Ive recently just added some eibach springs and with the run-shit tyres, i would say they are slightly firmer (on 20's). My guess is that once ive gone back to a normal tyre they will feel closer to the oem softness.
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      01-04-2021, 10:13 AM   #4
socalengineer
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Quote:
Originally Posted by doggboy View Post
Just get some Eibach springs. They are just as comfortable as stock, in fact I would have preferred them to be a bit more stiff.
The Billstein Pro Kit actually comes with Eibach springs. But the dampening will definitely be stronger because I believe it is the B8 strut.

I'm against just putting springs on the car because:
1) The dampening and spring rate need to be tuned for each car. Just upgrading the springs modifies this symbiosis leading to sub-par ride quality.
2) It puts extra stress on the strut because the strut was designed for a longer resting position.
3) It's not THAT much more expensive for the shocks + springs. Granted shocks are the majority of the cost.
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      01-04-2021, 09:05 PM   #5
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Quote:
Originally Posted by socalengineer View Post
The Billstein Pro Kit actually comes with Eibach springs. But the dampening will definitely be stronger because I believe it is the B8 strut.

I'm against just putting springs on the car because:
1) The dampening and spring rate need to be tuned for each car. Just upgrading the springs modifies this symbiosis leading to sub-par ride quality.
2) It puts extra stress on the strut because the strut was designed for a longer resting position.
3) It's not THAT much more expensive for the shocks + springs. Granted shocks are the majority of the cost.
You are over thinking things.

1. The stock shocks are adjustable via mode and the Eibachs are progressive springs just like stock, just one inch shorter. The rates change slightly in the coil.
2. The suspension is designed to travel several inches, and perform across various occupant weights. If you think a resting height of an inch lower is different stress on the suspension than having 3 passengers, think about things more from an engineering stand point. If you add aprox. 600 lbs the ride will be lower. The suspension is designed for that.
The question is what the castor and camber will be at the lower height. And i can assure you that a one inch drop is still able to be aligned to factory specs.
3. Eibach springs are about $250 US from the factory. Using aftermarket shocks means you lose the adaptive suspension settings.

Normaly i would agree with your points, as i have lowered and modified many cars, but in this case, unless you want to go coilovers, just swapping springs is the way to go.

Last edited by doggboy; 01-05-2021 at 09:32 AM..
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      01-04-2021, 11:18 PM   #6
socalengineer
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Quote:
Originally Posted by doggboy View Post
You are over thinking things.

1. The stock shocks are adjustable via mode and the Eibachs are progressive springs just like stock, just one inch shorter. The rates change slightly in the coil.
2. The suspension is designed to travel several inches, and perform across various occupant weights. If you think a resting height of an inch lower is different stress on the suspension than having 3 passengers, think about things more from an engineering stand point. If you add aprox. 600 lbs the ride will be lower. The suspension is designed for that. The question is what the castor and camber will be at the lower height. And i can assure you that a one inch drop is still able to be aligned to factory specs.
3. Eibach springs are about $250 US from the factory. Using aftermarket shocks means you lose the adaptive suspension settings.

Normaly i would agree with your points, as i have lowered and modified many cars, but in this case, unless you want to go coilovers, just swapping springs is the way to go.
1. Just checked the Eibach website they state their springs for the 640i application are suitable for the stock shocks.

However, I have seen many forum posts where users have blown their stock shocks with other lowering springs. So it's best to reference every specific application.

3. If you use coilovers you also loose adaptive suspension settings. I personally don't care too much for comfort/sport mode changing the dampeners but I can see if you're a user of them that would be a consideration.

I think running the eibach springs without the higher dampening from the B8 bilsteins wouldn't provide me the performance I am seeking. (which is what you mentioned that it is still not stiff enough with factory dampers)

I don't know anyone running ksports and don't know how they tune their suspension compared to Bilstein.
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      01-05-2021, 10:34 AM   #7
socalengineer
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FYI I asked the different manufacturers for their spring rates for the 640i application. Of course it is not comparable as you also need to take into account dampening. But here are the facts.

Eibach:
front = 268 lbs/in
rear = 171 lbs/in

KW v3:
Front: 510 lbs/in
Rear: 185 lbs/in

What's interesting is that the KW v3 setup lists the same coilover part number for the 650i and the 640i. The 650i has an additional 245lbs on the front of the car, surprised they didn't tune a separate suspension for that. Bilstein has separate part numbers for the B12 pro-kit for 640i and 650i. Maybe because kw v3 you can set the rebound as needed?

Eibach does not list a lowering spring for the 650i on their website. But the Eibach springs interestingly are linear for this application.

KW v3s are progressive.

Last edited by socalengineer; 01-05-2021 at 06:12 PM..
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